Humoral immune response to oral rabies vaccination in raccoon kits: Problems and implications

Abstract

Little is known about the immunogenicity of RABORAL V-RG(®) (V-RG), an oral rabies vaccine, in raccoon kits (Procyon lotor). The objectives of this study were to characterize the immunogenicity of V-RG in young kits and investigate the potential impact of maternal antibodies on response to vaccination of nursing raccoon kits. Raccoon kits (n=30) were vaccinated at either 3 weeks of age, 7 weeks of age, or assigned as contact controls. Nineteen kits (73%) that were whelped by unvaccinated mothers responded to V-RG exposure (orally or indirect contact) by production of detectable rabies virus neutralizing antibodies (RVNA) while 7 (27%) kits did not respond to V-RG exposure. Four kits were whelped by a mother with high levels of RVNA and all four kits acquired maternal rabies antibodies. At approximately 9 months of age, all kits were inoculated with a killed rabies vaccine, IMRAB3(®). The kits which initially responded to V-RG oral vaccination or contact with vaccinated littermates demonstrated a rapid anamnestic response. In contrast, the V-RG non-responders and those with acquired maternal antibodies exhibited a primary immune response to IMRAB3(®), where RVNA levels were substantially lower on days 5 and 7 than the levels in the animals with an anamnestic response. These findings suggest that the naïve contact kits and the nonresponsive kits most likely remained susceptible to rabies virus infection whereas the ones demonstrating response to V-RG would not have been susceptible to a rabies virus infection.

Variation in host home range size decreases rabies vaccination effectiveness by increasing the spatial spread of rabies virus

“…Our simulations show seasonal disease dynamics driven by the influx of susceptible juveniles during the synchronous birth pulse in early April to mid‐May. Spring vaccination was less effective because it coincides with this birth pulse, when susceptible juveniles are not yet weaned and are unlikely to forage for and ingest oral vaccine baits (Fry et al, ). Fall vaccination was more effective because susceptible juveniles—who otherwise may have been infectious or incubating the virus—were immunized prior to natal dispersal.…”

Management and modeling approaches for controlling raccoon rabies: The road to elimination

“…This bait timing is also advantageous because maternal antibodies in juveniles would have waned by this time. Fry et al [58] estimated the half-life of maternal antibodies to be 10.5 days post-weaning, and the results of this study also suggested (although not definitively) that the presence of maternal antibodies could interfere with a young raccoon’s ability to properly respond to oral vaccination. Similarly, juvenile foxes demonstrated an impaired immune response during a challenge with RABV, even after maternal antibodies were no longer detected [60].…”

“…Juveniles are an important cohort to target, given that they represent a pulse of new susceptible individuals that are capable of driving transmission dynamics. During this time of year, natural food resources might become more limited, which increases the attractiveness of baits, and the vaccine baits are less likely to be impacted by extreme temperatures [58, 59]. This bait timing is also advantageous because maternal antibodies in juveniles would have waned by this time.…”

Oral vaccination of wildlife using a vaccinia–rabies-glycoprotein recombinant virus vaccine (RABORAL V-RG®): a global review

“…In another case, two adult raccoons housed with orally immunized cage mates developed low levels of RVNA and also survived rabies virus challenge [ 52 ]. Finally, half of non-vaccinated raccoons in contact with raccoons kits orally vaccinated with V-RG (10 8.2 PFU/animal) developed detectable RVNA, suggesting the possibility of limited horizontal vaccine transmission among kits through suckling or playing immediately after oral vaccination [ 57 ].…”

“…All animals remained healthy, seroconverted within 28 days, and resisted rabies virus challenge [ 52 ]. V-RG has also been administered orally to 3 to 7 weeks old raccoon kits without adverse events [ 57 ].…”